Free piston compressor system with double acting compressor piston



Dec. 1, 1964 H. BOLDT 3,159,330

FREE PISTON COMPRESSOR SYSTEM WITH DOUBLE ACTING COMPRESSOR PISTON Filed July 2, 1963 4 Sheets-Sheet 1 26 79a 16 If 20 T a? {I J #0 I 24 2/0 1 w e? l I l I cOrnbUS/I'On 33 chamber 8 6 5 WM as 77a 17 73 lalor 30 ,8 39

fm emon Dec. 1, 1964 H. BOLDT 3,1 ,330

FREE PISTON COMPRESSOR SYSTEM WITH DOUBLE ACTING COMPRESSOR PISTON Filed July 2, 1963 4 Sheets-Sheet 2 Fig. 2 34 Fig. .7

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Dec. 1, 1964 H, L -r 3,159,330

FREE PISTON COMPRESSOR SYSTEM WITH DOUBLE ACTING COMPRESSOR PISTON Filed July 2, 1965 4 Sheets-Sheet 3 Dec. 1, 1964 H. BOLDT 3,159,330

FREE PISTON COMPRESSOR SYSTEM WITH DOUBLE ACTING COMPRESSOR PISTON Filed July 2, 1963 4 Sheets-Sheet 4 Fly. 6

United States Patent FREE FKSTGN COMPRESSQR SYEa'iEM WliTH DOUBLE ACTHNG CGMlRESSGR PHSIGN Heinz Boidt, Beriin-Charlottenburg, Germany, assignor to Borsig Aktiengeselischaft, Eeriim'legei, Germany Filed Italy 2, 1963, $92. No. 292,501 Claims priority, appheation Germany E'uiy 6, E62 16 Claims. (Ci. 23056) The present invention relates to a free piston compressor system with double-acting compressor piston.

In my copending patent application, Ser. No. 290,145, filed June 24, 1963 (based on German patent application Ser. No. B 67 862 Ia/46a filed June 29, 1962), there has been described a free piston compressor system the motor part of which primarily comprises a free piston compressed gas generator, while the two parts of said system which are arranged as an image to each other and on opposite sides of a transverse plane of symmetry, each comprise a prime mover piston, a return piston, and a compressor piston. Each one of the said two parts has its pistons interconnected by a piston rod so that each part forms a rigid system. The motor part which is balanced in itself may represent a diesel engine or a gas diesel engine.

In order to obtain identical numbers of strokes per minute after the compressor parts have been connected to the structure, it is necessary that also the compressor parts are balanced. According to the above-mentioned copending application, this has been made possible by employing one side of the compressor pistons as working side, whereas the chambers on the back sides of said compressor pistons are employed for storing the work for the return stroke. In this way, not only a balancing of the compressor parts will be obtained but also the additional advantage that a compressed gas generator may easily be converted to or built as a compressor.

It is an object of the present invention to provide a free piston compressor which will not only take advantage of the above-mentioned advantages but will also be able considerably to increase the compressor output.

It is a further object of this invention to provide a free'piston compressor, in which the compressor piston may act as double-acting piston.

It is still another object of this invention to provide a free piston compressor as set forth above, which will reduce the necessary work for returning the compressor piston.

Still another object of this invention consists in the provision of a free piston compressor which will also be able to compensate for errors in dimension when producing a compressor unit.

As indicated above, it is the primary object of the present invention so to design the free piston compressor system of my above-mentioned copending patent application that the compressor pistons willact as doubleacting pistons. It will be appreciated that it is not possible merely to use the back side of the compressor piston for compressing purposes because its heretofore function, viz. to store the work for the return stroke, must be preserved. These difficulties have been overcome accordingto the present invention by connecting the outwardly directed sides of the compressor pistons with plungers which, in cylinders associated therewith, will with each working stroke store the return work for the compressor piston. Advantageously, the diameter of the respective plunger is selected in conformity with the diameter of the piston rod connecting the compressor piston with the return piston.

According to a further development of the present invention, the cylinder of the plunger piston is provided lice with a control opening which, through an overflow conduit is connected either to the pressure conduit of the compressor, or the suction conduit of the compressor, or to a foreign pressure source. If the overflow conduit is connected to the suction conduit of the compressor, the plunger piston has to have a diameter somewhat larger than that of the embodiment according to the invention in which the overflow conduit is connected to the pressure conduit of the compressor. In a corresponding manner, it is necessary to adapt the diameter of the plunger piston to the prevailing magnitude of the pressure when the overflow conduit is connected to a foreign pressure source.

If desired, a reducing valve maybe arranged in the overflow conduit. This brings about that the initial pressure during the compression of the gas enclosed in the plunger piston cylinder and thus at the same time the work stored for the return of the compressor piston, will be reduced.

According to the present invention, the structural dimensions of the plunger piston, especially its length, may be adjustable. The compressor piston may be displaceable on its piston rod. The axial location and/or the axial length of the control opening in the plunger piston cylinder may be variable and adjustable. The chamber for storing the return work for the compressor part may have connected thereto one or more additional chambers the dead space of which, which increases the space in the plunger cylinder, may be variable, if desired. To this end the additional dead space to the space of the plun er piston cylinder may be formed byone or more cylinders which communicate with said space of the plunger piston cylinder, and the pistons of which may be variable. The above-mentioned features may be employed individually or in combination with each other. All of these features serve two purposes dilfering from each other. By means of said features it is possible to compensate for errors in the dimensions when designing the machine unit. Furthermore, these features represent advantageous means by which the compressor may be adapted to diiferent gases to be compressed.

It will be appreciated that when operating the compressors with different gases, i.e. with gases of diiferent polytropic exponents, the course of the compression and expansion in the working chambers of the compressor will vary. This makes necessary special means by which the compressor can be adapted to the driving engine by controlling the stored work for the return of each compressor piston in such a way that also the compressor parts of the entire unit will obtain the character of machines balanced in themselves. Such relationships are, for instance, presented when earth-gases of diflerent earthgas fields are to be compressed with a free-piston compressor. The means for effecting such adaptation, viz. the additional space adapted to be connected to the plunger piston cylinder for increasing the dead space of said cylinder results in the particular advantage that it makes possible the control of the machine in condition of operation. If the machine or engine is to be employable universally, it is necessary that the above-mentioned possibilities of adaptation to the respective conditions of ope-ration, be effected.

The invention also envisions. the possibility of connecting the overflow conduit connected to the pressure conduit or suction conduit, or to a foreign pressure source, through suction valves with the chamber of the plunger piston cylinder, in which instance the suction valves are arranged at such a wall portion of the plunger piston cylinder which will not be swept by the plunger piston. Suction valves may also, in cooperation with control open- I V in length.

aisasso ings, be provided for conveying actuating fluid to the plunger piston cylinder.

For purposes of starting the entire unit, advantageously both compressor sides may be provided with a common pressure accumulator, oreach compressor side may have its own pressure accumulator, for instance, in the form of a compressed, air bottle. Such accumulator or accumulatorsmay be fed through a check valve by the overfiow'conduit and/ or from the' chamber of the plunger pis- .ton cylinder by the working gas of the compressor. 7 Such accumulator or accumulators may be connected to the chambers of the plunger piston cylinder through a conduit having incorporated therein a starting valve.

' The above outlined objects and advantages of the 'in 'vention will appear'more clearly from the following specification in connection with the accompanying drawings, in which: t

23 of the compressor cylinder 12. Cylinder lid 24 together with the plunger piston cylinder 22 confines a chamber 25 serving for accumulating or storing the return I work for the compressor part. In this Way, the necessary conditions are created to assure that also the compressor part can operate as a part balanced in itself of the entire unit'whereby the adaptability of the compressor. of the other motor part will be assured and the number of strokes per minute of the inotorpart-compressed gas pro FIG. 1 diagrammatically illustrates one half of a free piston compressor system with double-acting pistons according to the present invention.

' FIG. 2 shows the cylinder plunger piston system of FIG. 1 in greater detail and with a plunger piston variable compressor I FIG. 3 shows how the parts making up the plunger piston of FIG. 2 may be arranged in a difierent manner.

FIG. 4 illustrates a portion of the arrangement of FIG. 1 according to which the compressor piston is adjustable on the piston, rod pertaining thereto; 'FI GL S shows an arrangement similar to that of FIG.

4 but differin g therefrom in that the plunger piston and I V t the piston rod .form a single integral piece.

I 1 FIG. 6 illustrates an arrangement similar to that of FIG. 1 but differing therefrom. in that the overflow conduit is connected to the suction conduit of the compressor.

FIG. 7 showsan arrangement similar to that of FIG. 6

but differing therefrom in that the overflow conduit com- 'municates with a foreign pressure source.

Referring now to the drawing in detail, the free piston compressor system illus'tratedtherein comprises a combustion chamber 1 of. the prime mover which may be a diesel engine or a. gas diesel engine. Reciprocably mounted in the prime mover cylinder 2 is the prime mover piston 3' the outer end 4 of which. has connected thereto the return piston 5 which latter also may form a single piece with piston 23. Return piston 5 is reciprocable in a cylinder .6 the portion 7 of which servesfor compressing the scavenging air, whereas the portion 8 of cylinder 7" d'ucer will be maintained.

The overflow conduit 26 has one end thereof connected to the pressure conduit 16 while the other end of conduit 26 leads to the control opening 27 of plunger piston cylinder 22; A. pressure reducing valve 28 in overflow conduit 26 makes it possible to adjust the initial pressure for the compression in chamber 25. In this Way, the magnitude of the return-work stored in chamber for each return stroke for the compressor part can be adapted to the requirements of the respective conditions of operation.

been illustrated in FIGS. 2, 3 and 4.

Further possibilities of, adaptation and variation are furnished by the above mentioned additional means namely by changingthe structural dimensions of piston 21', by dis placeablyarranging compressor piston 11 on its piston rod 9, by varying the axial location and/or. length of the control opening 27 and byvarying the dead space of the plunger piston cylinder 22 to which end chamber 25 may be connected with one or more additional chambers which 1 may individuallyor in groups beadded to chamber 25 and of which one or more may be varied as to size. This may be elfectecl for instance by forming the additional chamher by a'cylinder piston system the piston of whichmay be adjustable.

The above outlined possibilities of. modification have One embodiment'of varying the structural dimensions of the plunger piston 21 is illustrated in FIGS. 2 and 3.

In these figures, the reference numeral 21a designates the Y piston rod which at that end thereof which is shown in thedrawingias beingb'rokenis connected to the compresrepresents the chamber for storing or accumulating the return work for the motor part 2, 3. A piston rod 9 passes through a seal 10 and connects the return piston 5 to the compressor piston 11 which latter has been designed as double acting compressor piston. Compressor piston 11 is' reciprocable in a compressor cylinder 12. That end race of cylinder 12 which faces toward the transverse plane of symmetry X-YEof thesystem is closed by a cylinder head or cylinder lid 13. The chambers 14 and Smay also be located adjacent to each other in such a way that a common cylinder head closes both said cham- 1 bets Sand 14 as shown in FIG. 1 The other end of the compressor cylinder 12 is' closed by a cylinder head or' cylinder lid 23. The two working chambers 14 and 14a of thecompressor are connected to a suction conduit 15 and to a pressure conduit 16. This connection is elfected at the side of the suction line through branchconduits 17, 17a and suction valves 18, 18a. On the side of the presthrough branch conduits 19, 19a and pressure valves 29,

20a. The outer end face 11a of. the compressor piston 11 has connected thereto a plunger piston 21. This plunger piston21 may, if desired, alsoform the direct extension of piston rod 9 which in such an instance would extend through the compressor piston 11. Such an arrangement is illustrated in FIG. 5.

sor piston 11 of FIG. 1 or a part thereof. Mounted on the reduced portion 21b of the piston rodiare two semipistons 21c and two spacer members 21d which are pressed together by means of a hexagon nut Zle and in assembled condition form the plunger piston 21 of FIG. 1. By arranging the said :part-s indifferent sequence, one behind V theother, the axial lengthland the location of the plunger v piston maybe varied. The plunger'piston is as to its length and position :formed functionally by the sealing.

members, in this instance for example piston rings 21 The number of the piston parts and of the spacer members maybe adapted to the respective requirements.

FIG. 2 shows an embodiment illustrating the possible change .in the axial location and/or length of thecontrol opening 27. The illustrated opening 26b represents the opening where'the overflow conduit of FIG. 1 leads into an overflow chamber 26a. which latter communicates with chamber 25, for instances by bores 27a-27d. These bores 27tz-27d represent the control opening. The illustrated Y embodiment comprises four bores of which the respective outer bores are adapted to beclosedby valves 34a and 34!). FIG. 2 shows these valves in closed condition.

sure conduit '16, the respective connection is'effected I As will be evident from the drawing, plunger piston 21 i is reciprocable in a cylinder 22 connected to the Outer lid When piston 21 moves in the direction from B to -A, the

compression of'the gas volume starts in chamber 25 when thatedge lot the first piston ring which facesA sweeps An embodiment which makes possible to vary the dead chamber of the plunger piston cylinder 22 by steps or in a stepless manner is likewise illustrated in FIG. 2. Chamber 25a communicates through a bore a with the chamber 25. This chamber may be formed by casting onto the cylinder 22 a housing 36a or, if desired, a housing 5-61) may be bolted thereto.

By means of the handwheel 37 and a spindle 33 it is possible to move piston rod 39 which is connected to a piston 40. The piston is, for instance, sealed with regard to the cylinder wall by piston rings. By rotating the handwheel 37 it is thus possible steplessly to vary the volume of chamber 25:: from a minimum capacity to a maximum capacity which capacity is determined by the dimensions and the possible piston stroke. Piston 40 may be moved by hand, by means of a spindle or by electric or hydraulic motors through spindles or gear racks. Also remote drives are possible. Chamber 25b illustrates an additional chamber which is not steplessly variable. This additional chamber is connected through bore 35b with chamber 25. This bore 351) may by means of valve 41 selectively be opened or closed. In this way a non-steplessly variable additional or auxiliary chamber will be obtained. With regard to the housing connected to or bolted to the cylinder 22 and with regard to the drive, the same remarks set forth in connection with the chamber 25a apply.

An embodiment in which the compressor piston 11 of FIG. 1 is displaceable on piston rod 9 is shown in FIG. 4. In this figure, piston rod 9 has a reduced portion 9a with a threaded section 91) onto which the plunger piston 21 has been screwed. Between piston rod 9 and plunger piston 21 there are clamped in the compressor piston 11 and for instance two spacer member-s 11d. By varying the number of the spacer members lid on both sides of the compressor :piston 11, the latter may be axially displaced or located at different locations.

In conformity with the specific requirements, more or less than two spacer members may be provided. The said spacer members do not need to have the same axial length.

FIG. 5 shows an embodiment according to which the piston rod 9 and the plunger piston 21 of FIG. 4 have been designed as a single integral piece 21/9. With this design, the compressor piston 11 is by means of a threaded nut 9d clamped against a collar 9c. By means of spacer members 111:, the piston may be axially located at different locations. In conformity with the desired design, the locations of the collar 91) and the threaded nut fid may also be exchanged.

The starting of the machine may be adapted to the particular conditions of the entire unit. To this end, the pressure accumulator 29, for instance a pressure bottle may be provided. Each side of the unit may have associated therewith such a pressure accumulator. sure accumulator is, by means of a conduit 30 having a check valve 31 interposed therein, connected to conduit 32 from where the filling of the pressure accumulator 29 may be effected. Conduit 32 leads from the pressure accumulator 29 to the chamber 25 of cylinder 22. By opening the starting valve 33 in conduit 32, the chambers 25 on both sides of the unit will be acted upon by the compressed gas required for initiating the starting moveent of the unit. The gas loading the pressure accumulator 29 may also be withdrawn from the overflow conduit 26.

FIG. 6 illustrates an embodiment according to which overflow conduit 260 communicates with suction conduit 15, whereas according to FIG. 7 overflow conduit 26d communicates with a foreign pressure source.

As will be evident from the above, the present invention combines the advantages of high compressor output obtained by the double acting compressor piston with the adaptation of the compressor part balanced in itself to the likewise balanced motor part inasmuch as the The pres- 6 chamber for accumulating or storing the return Work of the compressor part is located outside the compressor cylinder.

Both halves of the unit on opposite sides of the transverse central plane X may, for purposes of obtaining a synchronous counter running condition of its two parts each consisting of the rigidly interconnected parts 3-59-1121 be coupled to each other by structural elements'known per se, for instance of the type disclosed in French Patent No. 1,283,892.

The pressures in the individual chambers may for instance be as follows: In chamber 1 approximately 1-80 atmospheres, in chamber 7 approximately 1-1.4 atmospheres, in chamber 8 approximately 1-4.2 atmospheres, in chambers 14, 14a approximately 2060 atmospheres and in chamber 25 approximately 150 (up to atmospheres.

It is, of course, to be understood that the present invention is, by no means, limited to the particular structural arrangement and elements described above but also comprises any modifications within the scoop of the appended claims.

What I claim is:

1. A free piston compressor system having two axially aligned cylinder piston :systems arranged as an image to each other on opposite sides of a plane of symmetry transverse to the axes of said cylinder piston systems, each of said cylinder piston systems when viewing from said plane of symmetry in axial direction of the respective cylinder piston system including: a prime mover cylinder, a prime mover piston reciprocable in said prime mover cylinderQa return cylinder, a return piston reciprocable in said return cylinder and connected to said prime mover piston so as to be movable thereby in one direction and to move said prime mover piston in the opposite direction, a compressor cylinder, a double-acting compressor piston reciprocable in said compressor cylin-' der, connecting rod means connecting said return piston to one side of said compressor piston, an auxiliary cylinder, and a plunger reciprocable in said auxiliary cylinder and connected to the other side of said compressor piston, said auxiliary cylinder being provided with means for admitting pressure fluid to that side of said plunger which is remote from said compressor piston.

2. An arrangement acording to claim 1, in which the diameter of said plunger corresponds to the diameter of said connecting rod means connecting said return piston to one side of said compressor piston.

3. An arrangement according to claim 1, in which said plunger is adjustable as to at least one structural feature thereof.

4. An arrangement according to claim 1, in which said plunger is adjustable as to its length.

5. An arrangement according to claim 1, in which said compressor piston is adjustable on the connecting rod means connected thereto.

6. A free piston compressor system according to claim 1, which includes additional chamber means connectable to said auxiliary cylinder and variable in volume.

7. A free piston compressor system according to claim 1, which includes at least one cylinder piston arrangement connectable to said auxiliary cylinder and variable in volume to thereby selectively vary the space for storing the return Work for said compressor piston.

8. A free piston compressor system having two axially aligned cylinder piston systems arranged as an image to each other on opposite sides of a plane of symmetry transverse to the axes of said cylinder piston systems, each of said cylinder piston systems when viewing from said plane of symmetry in axial direction of the -respec tive cylinder piston system including: a prime mover cylinder, a prime mover piston reciprocable in said prime mover cylinder, a return cylinder, a return piston reciprocable in said return cylinder and connected to said prime mover piston so as to be movable thereby in one direction and to move said prime mover piston in the opposite direction, a compressor cylinder having a suction conduit and also having a pressure conduit for com veying thereto compressed air, a double-acting compressor piston reciprocable in said compressor cylinder, con

necting rod means connecting said return piston to one j side of said compressor piston, an auxiliary cylinder, a

' 14. Alfrce piston compressor system havingltwo axially aligned cylinder, piston systems arranged as an image a to each other on opposite sides of alplane of symmetry,

transverse to the axes of said cylinder pistonsystems,

each of said cylinder piston systems when viewing from said plane of symmetry in axial direction of the respective cylinder piston system including: a prime mover.

plunger reciprocable in said auxiliary cylinder-and con-" nected to the other side of said'compressor piston, said auxiliary cylinder being provided with means for admitting pressure fluid to that side of said plunger which is remote from said compressor piston, said auxiliary cylinder being provided With a control opening, and overflow conduit means leading from said control opening to one of said conduits of said compressor cylinder.

9. An arrangement according to claim 8, which in cludes a reducing va-lve arranged in said overflow 'conduit means.

10. An arrangement according to claim 8, in which the position of said control opening is adjustable relative to said auxiliary cylinder. 7 f. I

11. An arrangement according to claim 8, in which the axial length of said control opening is adjustable.

12. An arrangement according to clairnB, whichv includes suction valve means for connecting said'overflow conduit means with said auxiliary cylinder, said suction valve means being so located in said auxiliary cylinder that it cannot be closed by said pltu'iger.

13. A free piston compressor system having two axially aligned cylinder piston systems arranged as an image to each other on opposite sides of a'piane ofsymmetry transverse to the axes of said cylinder-piston system,

each of said cylinder piston systems when viewing from said plane of symmetry in axial direction of the respective cylinder piston system including: a prime mover cylinder, at prime mover piston reciprocable in said prime mover cylinder, a return cylinder, a return piston reciprocable in said return cylinder and connected to said prime mover piston so as to be movable thereby in one direction and to move said prime'mover piston in the opposite direction, a compressor cylinder, a double-acting compressor piston reciproca'ble in said compressor cylinder, connecting rod means connecting said return piston to onedside of saidcompressor'piston, an auxiliary cylinder, and a plunger reciprocable in'said auxiliary cylinder, said auxiliary cylinder being provided with means for admitting pressure fluid to that side of said plunger whichis remote from said compressor piston, said auxiliary cylinder also having a control opening for connec-v tion with a fluid pressure source.

cylinder, a prime mover piston reciprocab-le in said prime mover cylinder, a return cylinder, a return piston reciprocable in said return cylinder and connectedto said prime mover piston so as to be movable thereby in one direct-ion and to move said prime mover piston in the opposite direction, a compressor cylinder having a suction conduit and also having a pressure conduit for conveying thereto compressed air, a double-acting compressor piston reciprocable insaid compressor cylinder, connecting rod means connecting said return piston totone' side of said compressor piston, an auxiliary cylinder, a'i

plunger reciprocable in said auxiliary cylinder and connected to the other side of said compressor piston, said auxiliary cylinder being provided with means for ad-' mitting pressure fluid to that side of said plunger which is remote from said vcompressor piston, said auxiliary cylinder being provided with a control opening, overflow conduit meansleadingiirom said control opening 15. An arrangement according to 14, which in-,

cludes a feeding conduit leading from said overflow conduit' means to said pressure accumulator means for charging the same.

16. An arrangement according to claim 14, which includes a 'feeding conduit leading from said auxiliary cylinder to said pressure accumulator means for charg ing the same.

References Cited in the file of this patent V UNITED STATES PATENTS 1,481,358 Dwyer Jan; 22, 1924 2,075,133 Pescara Mar. 30, 1937 2,189,497 Pescara Feb. 6, 1940 2,429,948 Steiner Oct. '28, 1947p 

1. A FREE PISTON COMPRESSOR SYSTEM HAVING TWO AXIALLY ALIGNED CYLINDER PISTON SYSTEMS ARRANGED AS AN IMAGE TO EACH OTHER ON OPPOSITE SIDES OF A PLANE OF SYMMETRY TRANSVERSE TO THE AXES OF SAID CYLINDER PISTON SYSTEMS, EACH OF SAID CYLINDER PISTON SYSTEMS WHEN VIEWING FROM SAID PLANE OF SYMMETRY IN AXIAL DIRECTION OF THE RESPECTIVE CYLINDER PISTON SYSTEM INCLUDING: A PRIME MOVER CYLINDER, A PRIME MOVER PISTON RECIPROCABLE IN SAID PRIME MOVER CYLINDER, A RETURN CYLINDER, A RETURN PISTON RECIPROCABLE IN SAID RETURN CYLINDER AND CONNECTED TO SAID PRIME MOVER PISTON SO AS TO BE MOVABLE THEREBY IN ONE DIRECTION AND TO MOVE SAID PRIME MOVER PISTON IN THE OPPOSITE DIRECTION, A COMPRESSOR CYLINDER, A DOUBLE-ACTING COMPRESSOR PISTON RECIPROCABLE IN SAID COMPRESSOR CYLIN- 